1. Technical Field
This invention relates to a packer for sealing against a wellbore wall.
2. Related and Prior Art
In the recovery of hydrocarbons, i.e. oil and/or gas, production wells are drilled through which hydrocarbons can be produced from a subsurface geological formation. In many cases, one or more injection wells are also drilled, into which fluid is injected for increasing the pressure and/or delivering chemicals to facilitate the production of hydrocarbons. Similar wells are drilled in geothermal plants as well.
Typically, a well is created by drilling a borehole into an earth formation using a drill string carrying a rotating drill bit, retrieving the drill string, lowering a casing into the borehole, and cementing the casing in place. When the cement has set, another smaller diameter drill bit is run through the casing to drill a further segment of the borehole and then retrieved, and then another casing is cemented in place in the formation. The process is repeated until a desired depth has been reached, which process additionally may include the drilling of offset wells, installation of valves, tubing, and other equipment. It is not always necessary to case the entire well.
The process of preparing a well for production is referred to as “completion,” and a person skilled in the art will be able to ascertain several details which are not discussed in any detail herein. In the following, the term “wellbore” is used for referring to both an uncased, “open” borehole, as well as to a cased borehole. In both cases the inner surface of the wellbore, i.e. the wellbore wall, may have depressions or elevations therein due to, for example, holes knocked into the rock by the drill string, corrosion of a casing, or wax and lime deposits, also referred to as “scale.”
A well may be divided into zones. For example, a wellbore could be drilled to penetrate two production layers, and be divided into two zones by plugs below and above the production layers as well as a plug between the layers. The plug seals off the annulus between an inner pipe and the wellbore wall. During the completion process, it may be desirable to supply sand or chemicals down the inner pipe into the lowermost zone. The plug located between the zones is then subject to a pressure from below. Thereafter the process is repeated for the next zone. The plug between the zones is then subject to a pressure from above. Thus, a plug serving this purpose is subject to pressure from both sides, and therefore has to seal in both directions. Additionally, regulations and standards exist which dictate that such plugs must seal in both directions. Wedge anchors for keeping the plug in place in the wellbore wall as well as other known components of the plug are not comprised by the present invention, and are therefore not described in any detail herein.
U.S. Pat. No. 2,399,766 (Steward, 1946) discloses a plug sealing against a pipe wall by means of an elastic sleeve which is compressed axially and thereby expands radially against the wellbore wall. If the wellbore wall contains depressions, the sleeve material on both sides of the depression will tend to pull the sleeve radially out from the depression and hence counteract the seal. Similarly, in the case of an elevation in the wellbore wall, the elastic material will try to pull the sleeve radially inwards in the vicinity of the elevation. In other words, an additional force is necessary to press an elastic sleeve into depressions and to prevent leakage around elevations. These problems are aggravated if the sleeve is made of a rigid rubber compound designed to resist high pressures and temperatures in the deep wells drilled nowadays. Steward also discloses numerous variants of setting mechanisms in which a leading screw and nut are rotated relative to each other to effect an axial movement between the screw and nut. The axial movement is used for activating wedge anchors in addition to the elastic sealing sleeve.
It is an object of the present invention to provide an improved seal between a mandrel and a wellbore wall. The mandrel may be compact and prevent any fluid flow therethrough, or be a pipe allowing fluid to flow through an inner, longitudinal passage in the mandrel.